The present invention relates to measuring devices and, in particular, to electro-optical length and angle measuring devices which employ an incandescent lamp mounted on a fram. Such measuring devices are commonly used to measure the relative movement between moveable parts in machines such as machine tools.
Various electro-optical measuring devices of the prior art employ an incandescent lamp which is rigidly mounted to a scanning unit so as to illuminate a measuring scale. When such measuring devices are mounted on machine tools, they are often subject to damage from shocks and vibrations associated with machine tool operation. In particular, incandescent lamps have lamp coils which may tend to oscillate at a resonant frequency, and when an applied vibration is at or near the resonant frequency of the lamp coil, the coil will often vibrate at large amplitude and eventually break. This, of course, generally renders the measuring device inoperative and necessitates the replacement of the lamp.